Modern telecommunications networks generally include two separate communication pathways or subnetworks. The first is a voice network that handles the transmission of voice or other information between users. The second is a signaling network that facilitates the dynamic linking of a plurality of voice network circuits, such that a voice-type connection is established between a calling party and a called party. These functions are generically referred to as call setup and call teardown. Additionally, the signaling network provides a framework through which non-voice related information may be transported in a manner that is transparent to the user. This signaling technique is often referred to as "out of band" signaling, where the term "band" implies voice band. Common examples of such out of band data transport are the access of 800 number database services, calling card verification services and caller ID services.
In order to provide consistent and reliable communication across the signaling network infrastructure, a common or standard digital signaling protocol known as Signaling System 7 (SS7) has been developed. SS7 is an out of band common channel signaling system that uses labeled messages to transport circuit related signaling information, non-circuit related signaling information, network resident database service information and other information that may be used for the establishment of communication services.
From a hardware perspective, an SS7 network includes a plurality of SS7 nodes, generically referred to as Signaling Points (SP), that are interconnected using signaling links, also referred to as SS7 links At least three types of SPs are provided in an SS7 network: Service Switching Points (SSP), Signal Transfer Points (STP) and Service Control Points (SCP).
An SSP is normally installed in tandem or Class 5 offices. The SSP is capable of handling both in-band signaling and SS7 signaling. An SSP can be a customer switch, an end-office, an access tandem and/or a tandem. An STP transfers signaling messages from one signaling link to another. STPs are packet switches and are generally installed as mated pairs. Finally, SCPs control access to databases such as 800 number translation, 800 number carrier identification, credit card verification, etc.
Signaling datalinks are transmission facilities used to connect SPs together. They are dedicated bidirectional facilities operating at 56 kbps in the U.S. and Canada and at 64 kbps when clear channel capability is deployed. Normally, every link has a mate for redundancy and enhanced network integrity.
Signaling datalinks include access links or "A" links that connect SSPs to STPs and that connect SCPs to STPs, as shown in FIG. 1. Bridge links or "B" links are used to connect mated STPs to other mated STPs that are at the same hierarchical level, as shown in FIG. 2. Cross links or "C" links connect mated STPs together, as shown in FIG. 3. They are used for passing messages between STPs when signaling network failures are encountered.
Diagonal links or "D" links connect STPs of different hierarchical levels, as shown in FIG. 4. Extended links or "E" links connect SSPs to STPs that are not within their associated local STP area, as shown in FIG. 5. Finally, fully associated links or "F" links connect SSPs directly together without STPs, as shown in FIG. 6. FIG. 7 is a block diagram of a two-level SS7 network including a summary of possible link deployment.
SS7 also includes a network protocol. As a protocol, SS7 defines a hierarchy or structure of the information contained in a message or data packet that is transmitted between SPs of an SS7 network over signaling links. This internal data structure is often referred to as an SS7 protocol stack which includes the following four SS7 levels:
Level 1: The Physical Level PA1 Level 2: The Datalink (or Link) Level PA1 Level 3: The Network Level PA1 Level 4: The User Level
The physical level, also referred to as the Message Transfer Part (MTP) level 1, is the lowest or most fundamental level and is the first level that is used to interpret and process an incoming message. This level determines and/or provides the electrical characteristics to transmit the digital data over the interface being used. Following interpretation/processing, the incoming message is passed up the stack to the datalink level.
The datalink level, also referred to as MTP level 2, resides adjacent and above the physical level and is responsible for providing the SS7 link with error detection/correction and properly sequenced delivery of SS7 message packets. Following interpretation/processing, the incoming message is passed up the stack to the network level.
The network level, also referred to as MTP level 3, resides adjacent and above the datalink level and is responsible for message packet routing, message packet discrimination, and message packet distribution. Functionally, message discrimination determines to whom the message packet is addressed. If the message contains the local address of the receiving SP, then the message is passed on to message distribution. If the message is not addressed to the local SP, then it is passed on to the message router. Following interpretation/processing, the incoming message is passed up the stack to the user part level.
The user part level resides adjacent and above the network level. The user part level may include many distinct parts including a Transaction Capability Application Part (TCAP), an ISDN User Part (ISUP), and a Signaling Connection Control Part (SCCP).
The above description has assumed that an incoming message is being processed. An outgoing message is passed through the protocol stack in the opposite direction, entering at the user part level and exiting from the physical level. FIG. 8 illustrates SS7 protocol architecture relative to SS7 levels and relative to standard Open System Integration (OSI) layers. The hardware elements and protocols of an SS7 network are well known to those having skill in the art, and need not be described further herein.
A high performance STP is marketed by the assignee of the present application as the Eagle.RTM. STP. A block diagram of an Eagle.RTM. STP is shown in FIG. 9. A detailed description of the Eagle.RTM. STP may be found in the Eagle.RTM. Feature Guide PN/9110-1225-01, Rev. B, January 1998, published by Tekelec, the disclosure of which is hereby incorporated herein by reference. As described in this publication, an Eagle.RTM. STP 900 includes the following subsystems: a Maintenance and Administration Subsystem (MAS) 910, a communication subsystem 920 and an application subsystem 930. The MAS 910 provides maintenance communications, initial program load, peripheral services, alarm processing and system disks. The communication subsystem 920 includes an Interprocessor Message Transport (IMT) bus that is the main communication bus among all subsystems in the Eagle.RTM. STP 900. This high speed communications system functions as two 125 Mbps counter-rotating serial buses.
The application subsystem 930 includes application cards that are capable of communicating with the other cards through the IMT buses. Three types of application cards are presently included: a Link Interface Module (LIM) 950 that provides SS7 links and X.25 links, an Application Communication Module (ACM) that provides a TCP/IP interface over Ethernet, and an Application Service Module (ASM) 940 that provides global title translation, gateway screening and other services. A Translation Service Module (TSM) may also be provided for local number portability.
The LIM provides level 1 and some level 2 functions on SS7 signaling links. The ACM provides access to a remote host for an STP LAN feature, described below. The ACM provides unidirectional access from the STP to a remote host for the STP LAN feature. Unidirectional connection from the STP to a host is provided through an Ethernet LAN using TCP/IP protocol. Finally, the ASM provides additional memory that is used to store translation tables and screening data. A detailed description of the Eagle.RTM. STP is provided in the above cited Feature Guide and need not be described in detail herein.
A brief conceptual overview of the Eagle.RTM. STP is provided in the brochure entitled Eagle.RTM. STP Platform, Publication 908-0126-01, Rev. A, Tekelec, 1997. As described therein, the Eagle.RTM. STP is a high capacity, fully fault tolerant packet switch and self-contained local area network for exchanging data messages between a half-dozen to several hundred or more message processing modules. In the Eagle.RTM. STP system architecture, three functionally specific application subsystems access each other via a communications subsystem which includes dual counter-rotating, 125 Mbit/sec. IMT buses. The application subsystems include LIMs that provide SS7 and X.25 access to telecommunication signaling networks, ACMs that provide TCP/IP access to local area networks and a MAS that provides maintenance communication, peripheral services alarm processing and system disks. As stated in this brochure, "ACMs communicate directly with external, collocated service application systems via a TCP/IP, 10 Mbit/sec. LAN interface mounted on the Ethernet Interface Applique (EIA). Examples of external application systems include: an SCP not equipped with SS7 signaling links, a routing or charging database system, cellular/PCS home or visitor location registers (HLR, VLR), a message accounting system, a voice/record/image processing system, and other IN service nodes and peripherals that require direct interface via SS7 signaling links."
A detailed description of the operation of the Eagle.RTM. STP-LAN interface feature, which actually provides an ACM that communicates with an external LAN, is provided in the brochure entitled Eagle.RTM. STP STP LAN Interface Feature, Publication 908-0134-01, Rev. B, Tekelec 1997. As described therein, "The STP-LAN Interface Feature enables the collection of copies of SS7 messages that transit the EAGLE STP. This feature, along with user-provided data processing equipment, allows the EAGLE to perform functions beyond normal Signal Transfer Point (STP) functionality, such as auditing and accounting functions, message trap and trace and protocol conformance analysis. The EAGLE STP-LAN Interface Feature enables the user to connect external data collection or processing systems directly to the EAGLE STP via TCP/IP, 10 Mbits/sec. Ethernet LAN. It enables a user to select either ISUP messages, SCCP/TCAP messages, or both, for transfer to the external system. It also adds a time-stamp to identify the selected messages and their sequence for subsequent processing." As is also shown in this brochure, the Ethernet LAN link is a unidirectional link from the ACM to an external processor (host).
It is also known to interface an Eagle.RTM. STP to other networks using links other than SS7 links. For example, it is known to provide a database transport access feature that intercepts message signaling units originating from an X.25 network. See the brochure entitled Eagle.RTM. STP Database Transport Access Feature, Publication 908-0136-01, Rev. B, Tekelec, 1997.
It is also known to use protocol converters in connection with STPs. For example, the Eagle.RTM. STP X.25 Protocol Conversion Feature provides interfacing and connectivity between nodes on an SS7 network and nodes on an X.25 network. See the brochure entitled Eagle.RTM. STP X.25 to SS7-IS.41 Protocol Conversion Feature, Publication 908-0135-01, Rev. B, Tekelec, 1997. Similarly, it is known to provide an ANSI-ITU gateway to enable an Eagle.RTM. STP to interconnect to other types of signaling networks. See the brochure entitled Eagle.RTM. STP ANSI-ITU Gateway Feature, Publication 908-0133-01, Rev. B, Tekelec, 1997.
Protocol converters are also known for translating protocols between SS7 and non-SS7 networks. For example, the Tekelec SS7 -Frame Relay Access Device (FRAD) translates SS7 protocol information between an SS7 network and a frame relay network. See the brochure entitled SS7-Frame Relay Access Device SS7 Protocol Information Translator, Publication 908-0167-01, Rev. A, Tekelec, 1997.
Protocol conversion for SS7 networks is also described in U.S. Pat. No. 5,793,771 to Darland et al., entitled "Communication Gateway". This patent describes a system and method for protocol translation. The system includes an SS7 Module for sending and receiving a plurality of incoming and outcoming SS7 queries and responses. The system also includes an Inbound Subsystem Module, coupled to the SS7 Module, for translating the incoming SS7 queries from an SS7 protocol to a non-SS7 protocol. The translated incoming queries are forwarded to an end user while in the non-SS7 protocol. The Inbound Subsystem Module also translates any responses corresponding to the incoming SS7 queries from the non-SS7 protocol to the SS7 protocol. The system further includes an Outbound Subsystem Module, coupled to the SS7 Module, for translating outgoing SS7 queries from the non-SS7 protocol to the SS7 protocol. The translated outgoing queries are sent via the SS7 module across an SS7 network. The Outbound Subsystem Module also translates SS7 responses corresponding to the outgoing SS7 queries from the SS7 protocol to the non-SS7 protocol. The translated responses corresponding to the outgoing SS7 queries are forwarded to an end user while in the non-SS7 protocol. See also U.S. Pat. No. 5,706,286 to Reiman et al., entitled "SS7 Gateway" and U.S. Pat. No. 5,640,446 to Everett et al., entitled "System and Method of Validating Special Service Calls Having Different Signaling Protocols."
Unfortunately, the dedicated SS7 links that connect an STP to other SPs of an SS7 network can be capital intensive and expensive to maintain. Moreover, since redundant SS7 datalinks are generally used, the cost of these links can be even more capital intensive and expensive to maintain. These expenses can be a barrier to further expansion of wired telephone networks and/or cellular telephone networks.
For example, when cellular service providers enter a new geographic area or market, the cellular service providers generally need to connect the elements of a cellular radiotelephone network to the wired telephone network, also referred to as the Public Switched Telephone Network (PSTN). Therefore, a connection between a Mobile Switching Center (MSC) which is a type of SSP, and at least one associated STP, uses at least one SS7 A-link. Since most SPs are connected to the SS7 network via a mated pair of STPs, the number of the SS7 datalinks may double.
Similar considerations may apply to wired service providers that enter into or expand in a geographic area or market. The large number of SS7 links that need to be provided can increase the expansion cost for wired and wireless networks, thereby increasing consumer cost and/or reducing consumer access to competitive service providers.